US2265779A - Facsimile synchronizing device - Google Patents

Description

Dec. 9, 1941. K

1 H. c. REssLER `r".1&GSIMIL`.. SYNCHRGNIZING DEVICE Filed spt. `14, 1939 l 2 sheets-sheet'i R 1 Y mw ms, Mbo V3 H mm A* YW um. We WNW 9% .Y c NUM Dec. 9, 1941. H. c. REssLl-:R

FACSIMILE vSYNCHRONIZING DEVICE- I y "2- sheets-smetV 2 4Filed Sept. 14, 1939 lll IIIIIIIII'IIIIIIIII llllllllllllllllll lllllililllllllllll lllllllllllllllll mnmnn "ummm BY Y Y y ATTORNEW frequency.

`marking or picture signals.

Patented Dec. 9, 1941l UNITED STATES PATENT OFFICE f 2,265,779 f q i j FACSIMILE sYNcmioNrzlNG DEVICEv Hugh VCRtesSIer, RiehmondyN.v Y., assignor to Radio Inventions, Inc., New York, N. Y., a corporation oi New York y Application september 14, 1939, serial No. 294,868`

s claims. (ci. 17atati` The present invention concerns electrical/synchronizing systems and, in particular, electrical synchronizing embodying a novel method of frequency multiplication,

One object of the present inventionis to'provide' methods of and means for deriving essentially sine wave synchronizing signals of harmonic frequency from lower frequency signals.

Y Another object is to vderive these harmonicfrequency signals by methods and means which veliminate the Vfundamental without the use of conventional filters or oscillators at the harmonic A further object is to derive harmonic signals in `which any residual undesired component is spaced at least twice the fundamental frequency away from the desired harmonic. i

Astill further object isto derive substantially pure harmonic signals of any desired order and with simple changes to vary the order of the harmonic at will .without altering they efliciency of the system or the purity of the resultingy signal.

In facsimile, television yand similar systems,

synchronism must be maintained between the transmitter and receiver in order to be able to accurately record or reproduce the transmitted material. Economic considerations, in general, require that synchronizing signals be transmitted during short intervalsinterposed with the Since itis desirable to apply a continuous signal to the synchronizing means, especially if the latter comprises an electric motor, the spaces between the intervals of synchronizing signal transmissionmust be filled in. One method of filling in the-spaces isto generate trains of damped oscillations by shocking" an oscillatory circuit, resonant at the deslred synchronous frequency,.by `means of the transmitted synchronizingsignal. Final smoothing and elimination of harmonics may'be accomplishedLby resonant filters tuned to the desired harmonic. This method becomes increasingly ineiTlc-ient as the order of the harmonic increases and as the frequency decreases. PracticalA systems also leave some harmonics, especially those adjacent to the desired harmonic', which maybe a. source of disturbance in the synchronizing system. The present invention'concerns a system which approaches an ideal system andcompletely eliminates the difficulties pointed out above.

In the present system, low frequency impulses are transmitted interposed with facsimile vor other signals. Electrical vwaves having the fundamental frequency of these impulses are produced by means of a highly regenerative circuit or by synchronizing an oscillator. Two components of this low frequency, 90"v out of V phase,

may be -applied to deflecting means of' anV electhe target corresponds to the order of harmonic which is desired. The stream sweeping the target generates the desired harmonic frequency.

signal which is amplified and applied to the 'recorder or other synchronizingA means. Alternately the low frequency signal may be multiplied to a higher frequency 'by one or more frequency multiplyingv circuits consisting of single or multiple phase rectiflers. The multiplied frequency maybe applied directly to the synchronizing means or it may `be further multiplied b -applying it to the target multiplier. A l

The invention may be more fully understood and further objects willA be evident from the following detailed description-when taken in con- Junction with the variousxfigures of the drawings. Y

In the drawings: A Fig. 1 shows one form of the present invention applied to afacsimile receiver. f

Fig. 2 shows an enlarged diagram of of the apparatus shown in Fig. 1. y

. Fig. 3 shows diagrams of signals useful inexplaining the operation of Fig. 1.

Fig. 4 shows 'a modified portion ofthe circuit o'Fig..1. i l i Fig. `-5 shows diagrams of signals associated with the operation of Fig. 4. Y

alternatingfcurrent. Recordings are made byv means of a stylus 'I energized from -receiver I. synchronizing.. signalsfwhich will `usually be of the form a' and a in Fig. 3, are fed from receiver I to primary of transformer 9-II). The spacesbetween a' anda" willusually beoccupied by picture signals. The synchronizing vsignals a' a .fromthe receiver consist of a number of essentially constant amplitude cycles of 'subcarrier frequency voltage', the envelope of which is essentially rectangular.- These signals induce similar signals in secondary Ill of the coupling vtransformer and this secondaryl voltagefisapplied across rectiivier I I in series with loadIZ-IS thereby removing'the sub-carrier component and` 'leaving rectangular unidirectional impulses across load resistor I2 shunted by condenser I3.

one part- These rectangular impiuses are applied to grid u of a double tube I thru resistor I5. Tube I5 includes two sets of elements and may-be replaced by two separate tubes. One set of elle-- ments includes cathode I1, control grid |4 and plate I5, while the other set includes cathode i3, control grid 20 and `plate 2|. Each set of elements forms an amplifier stage. Cathode I1 receives a bias from current thru resistor 22 and plate I6 is loaded by resistor 23 and is energized from 'a source of direct current 24 having an internal resistance 25 and regulated by a voltage regulator 26. The second amplifier stage is con'- nected in cascade by feeding grid 25 from plate I3 thru coupling condenser 21 and across grid leak 26. Cathode I6 receives its bias from the cathode current drop in resistor 2 6 and lplate 2| is loaded by resistor 33'and is energized from direct current source 24.` A third stage of amplification is provided by tube 3| having cathode 32, control grid 33 and plate 34. Grid 33"re ceives an adjustable portion of the loutput of plate 2| thru coupling condenser 35 across gain control 36 from the adjustable tap 31. Cathode 32 is connected to bias resistor; 33 and plate-34 is loaded with resistor 35 and energized from source 24. Calling plate`34 the output ofthe three stage amplifier and grid I4 its input, a bridge network consisting of resistors 46, 4| and `44 and Vcondensers 42, 43 and 45 is connected between output and input. Resistor 45 in series with resistor 4I, is connected in parallel with condenser 42 in series with condenser 43, resistor 44 is connected in series with condenser and the two are connected between the junction between condensers 42 and 43 and the junction between resistors 46 and 4| to complete the bridge network. -The input is fed directly from plate 24 to, the

. junction between resistor 45 and condenser 42 and the output from .the Junction between resistor 4| and condenser 43 is fed to` grid |4 thru blocking condenser 19.` Since the bridge network passes currents of all frequencies, except those at the balance frequency, and there are an odd ,number of stages in the amplifier, the. amplifier condenser 43. Thus, the amplifying system is responsive to one frequency, the ybalance frequency, and if'this is made to be fo, the fo com ponent of rectified impulses al' and a" will be selected. The rectangular impulses produced by rectifying a and a may be represented mathematically by a series of terms consisting of fo and many harmonics due to the fact that a' and a" are spaced a distance to apart. ;4

yAlso, in Fig..1 is shown a special cathode ray tube 43 including .a cathode 49,- control grid 56, first anode 5|, second anode 52, deflecting plates 53, 54, 55 and 56 and a special target 51. 'Ihe second anode 52 is energized from direct current source 24 and first anode 5| is supplied with current from a tap on resistor 55 also supplied from source. 24. This tube produces an electron beam ldirected on totarget 51, and may be madeto be sharply defined yby proper adjustment of the focus control voltage on anode 5|. This beam is deflected by deflecting plates. and 56 in perpendicular directions. Target 51 acts asa anode and output voltage is takenod across load resistor 53 connected. between target 51 and source 24.

An enlarged view of the surface of target or anode 51 is shown in Fig. 2. The target is shown for a multiplication factor of 18 with 18 nonemitting segments 52 and 18 emitting Segments 63.A kThe target may be made of aluminum foil on which are formed carbonized segments. 52

leaving the aluminum exposed in segments 63.'

The electron beam striking target 51 generates a large number of secondary electrons when the beam strikes the emitting segments 33 and a very y few secondary electrons when it strikes the nonemitting segments 62. Thus. the beam in passing over the' segments generates an alternating current having a maximum when it is-"on the emitting segments and a minimum when on the non-emitting segments. v

Fig. 3 shows the modulated sub-carrier synchronizing impulses a and a fed into the trans-- former 3|5. Rectifier and its associated load |2-.|,3 remove the subcarrier and produce rectangular impulses equivalent to one-half of the envelope of impulses aand a". Thethree stage bridge-controlled ampliflersharply selects the fundamental frequency component having a period tolas vshown at a. f At points 45. and 41 of the bridge circuit of Fig. 1 there will exist two substantially pure sinewave voltages having periods ta'but having a phase difference of 90.as

`represented/by a and b. When the 'beam' -of cathode ray tube v46 is deflected by applying these 90? out of phase voltages to the perpendiculardelecting plates 54 and^56.it traces a circular pattern on target 51. The beam passing over the segments of target 51 generates in load -resistorv 53 asubstantially pure sine wave voltage of ay frequency nio where n is the'number of emitting or non-emitting segments and fo. is the frequency of the waves a and b'having the period to. Helo is for instance 3% cycles and -n is`18, then `the-generated frequency nfs will be 60 cycles. This 60 cycle signal is fed thru coupling condenser 60 across resistor "5| to the synchrol rent generated by. this unit.

nous alternating current generator 5 for purposes of synchronizing to 60 cycles the alternating cur- 'I'his generated synchronous alternating current is applied to motor 4. )If ymotor 4 is a two pole synchronous motor,

it will run at 60revolutions per second and if gear 6 reduces this speed 18-1, drum 5 will revolve 31/3 times per second and to will represent one scanning line. The synchronizing impulses will then be interspaced with lines of facsimile picture signal.. g

l Briefly, the process just described in detail consists in recapturing,in substantially pure sine form, the fundamental frequency: component of the synchronizing impulses and multiplying this fundamental by a desired factor to produce an vessentially pure harmonic frequency of the 4fundamental. This harmonic frequency 'is used vto synchronize an alternating current generator or is amplified tov produce alternating current of sutlicient power to drive a motor or other recorder driving means.

In Fig. 4 is shown a modified bridge circuit for generating a synchronizing signal in which the harmonic components are more widely Vspaced than if the fundamental frequency were distorted to produce the harmonic component desired. Distortion of the fundamental as by an overloaded amplifier produces undesired harmonic connecting a load consisting of resistor 1Sy components spaced by a frequency differencel equal to the fundamental frequency away from the desired harmonic. The system to be described yields undesired components spaced two or more times the fundamental away from the desired harmonic frequency.

Fig. 4 shows a circuit which may be used with the circuit of Fig. l by connecting lead 18 to plate 34 and lead 1| to one side of condenser 19 and produces an output at lead 18 which may be used as a synchronizing signal. Tubes Il, I5 and 3l of Fig. 1 may be used with the circuit of Fig. 4, but tube 48 will not ordinarily be required. The circuit includes the balanced feedback circuit of Fig. 1 employing resistors 40, 4I and condensers 42, 43 and 45. The balanced feed-back, when attached to the three stage amplier shown in Fig. 1, serves to recapture the fundamental of theisynchronizing impulses, as shown at a. and b of Fig. 5c. In Fig. 4 secondary 64 of transformer 64-66 isconnected between condenser 45 and ground G and secondary 65 is connected between resistor 44 and ground Gr I.

Secondaries 64 and 65 and their associated magnetic circuits are so proportioned that the transformer cores are well saturated by signals a and b, except near zero instantaneous value. Under these conditions the apparent inductance of pri-y maries B6 and 61 will be small except for intervals near zero fundamental voltage. If a represents the voltageacross resistor 44 and secondary 65, the apparent inductance of primary 61 will have the form shown at i. Similarly, if b represents the voltage across secondary 64, the

apparent inductance of primary 68 will have` the form shown at i. Now, if an audio frequency signal is applied from the audiosignal source through leads 68 and 69 to primaries 66 and 61 connected in series, these signals will be passed by transformer 65-61 during interval i and by transformer 64--66 during interval i. Thus, the voltage across secondary 65 will be of the form shown by Fig. 5d and the voltage across secondary 64 will be of the form shown by Fig. 5e. The envelopes of these signals have been drawn in on Fig. 5d and e to emphasize the fact that they consist of impulses of audio frequency voltage and are spaced by one-half' the period of the fundamental a or b. Voltages across secondaries 64 and 65 are combined and impressed on rectifiers 12 and 15 in series with resistors 13 and A bridge rectifier circuit is completed by shunted by condenser 11 from the junction between resistors 13 and 14 to ground G. The

audio frequency signals-across secondaries 64V and 65 are rectied and waves d produce rectified current impulses J while waves e produce rectified current impulses g. Impulses f and g are Y produced in the common load 16-11 and hence appear together at output point 18 to form a` It will be seen that the action of the systems described is to recapture the fundamental fre- 'quency of synchronizing impulses in essentially having a period integrally Vrelated to the period quency to produce synchronizing signals, While two methods ofaccomplishing this result have been shown and described, many'modiflcatlons will be evident to those skilled in the art within the spirit and scope of theinvention as set forth.

in the appended claims. s

' What is claimed is: y 1. In a synchronizing system, the combination of, a, source of limpulses comprising a fundamental frequency wave and large components of harmonics of said fundamental, a selective circuit for separating said fundamental frequency wave from saidharmonics to provide a substany tially pure sine wave of fundamental frequency, a frequency multiplier "responsive to said funda; mental for producing a wave having a predominant component harmonically related to said fundamentalfrequency, anda device to be synchronized responsive to said predominant harmonic component.` v

2. In a device for synchronizing a facsimile recorder with a predetermined series of syn-` chronizing impulses, the combination of, a recti-v fier for deriving Aunidirectional impulses from said synchronizing impulses, a selective. feed--l back amplifier for generating from said unidirectional impulses a substantially pure sine wave signal having a .period equal to the period of said impulses, a cathode ray tube having a segmented target for multiplying the frequency o f said sine wave signal to produce a signal of predetermined higher frequency, a recorder driven by a synchronous motor, and meanslfory generating an alternating current to operate said motor controlled by said higher frequency. 1 3. In a device for synchronizing a facsimile recorder in accordance with a series of substanrtially equally spaced impulses, the combination nal of a kpredetermined higher frequency, a reperiod equal to the period of said impulses, means y for multiplying thefrequency of said sine wave signal to produce a second signal having a pre-'1V determined higher frequency, a recorder driven by a synchronous type motor, andv means for operating saidl motory in synchronism with sa?,

second signal. s

5.-In a device for operating a facsimile rcorder'under control cfa series ci substantially equally spaced impulses, the combination` of, a

V. selectiveaperiodic circuitfor deriving from said impulses a substantially pure sine wave signal of said impulses, means'for multiplying the fre-L1 'f quency of said sinewave signal to produce ya second signal having i a predetermined higher.l frequency, a recorder driven by a synchronous.

fpureslne form and then to multiply the fre- HUGH c. REvssLEn. t

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